Stereoscopic range finder having stationary measuring marks



Jan. 25,l 1938. o. EPPENSTEIN STEREOS'CQPIC RANGE FINDER HAVING`STATIONARY MEASURNG MARKS Filed Sept. 30, 1936 In veh for:

Patented Jan. 25, 1938 UNITED! STATES STEREOSCOPIC RANGE FINDER HAVINGSTATIONARY MEASURING MARKS Otto Eppenstein, Jena, mesne assignments, toCompany. Rochester,

New York Germany, assignor, by Bausch & Lomb Optical N. Y., acorporation of Applicationiscptembcr'ao, 1936, serial No. 103,307 sGermany October 5, 1935 3 Claims.

I haveled an application in Germany,40cto ber 5, 1935 of which thefollowingis a specification.

The invention refers to a steroscopic rangender having in its iields ofview stationary marks that are to be so united in pairs stereoscopicallyas' to constitute a number of stereoscopic measuring marks at differentapparent distances, measurements being eiected by a comparison of thedistance of the viewed object and the apparent distances of thestereoscopic marks In the known rangeflnders of this kind, the singlemarks lie in the focal planes of the objectives. The fact, however, thatthe images produced by the objectives lie in the focal planes only whenobjects at innnity are concerned. and that near objects are imaged inthe rear of the said planes, very often entails a disturbing parallaxbetween the object images and the stereoscopic measuring marks, whichparallax may considerably falsify measurements especially when objectsat comparatively small distances are concerned.

The invention aims at overcoming this disadvantage by providing themeasuring marks in those planesin the rangeflnder in which the ob.- i

jectives image objects that are at such distances as correspond to therespective steroscopic marks, measuring errors dueto parallax beingreduced to innocuousness by merely approximating the said condition.Each measuring mark maybe disposed on a plano-parallel glass plate ofcorresponding thickness, and the glass plates of each iield of view 'may`be combined to a set of glass plates constituting a mark carrier. Itis, however, especially advantageous lto arrange the measuring marks ofeach of the two elds of view in one plane inclined relatively to thefocal plane of the corresponding objective. Accordingly, there may beused, for example, aA mark plate disposed in and inclined relatively tothe ray path. The said condition is easily arrived at by suitablydistributing the measuring marks on this inclined plane. The samepurpose is served, however, also by disposing the measuring marks on acurved surface of the mark carrier.

An especially simple construction is obtained by using as carriers forthe measuring marks ,plano-parallel plates-which consist of two glass'wedges traversed by the imaging rays subsequently to each other andhaving the marks on their cemented surfaces. Owing to the refraction ofthe rays by the glass wedges traversed last, an observerlooking into theeye-pieces perceives the marks as lying in planes which are lessinclined to the focal planes of the objectives than the cementedsurfaces. If, as is the case generally, the eye-pieces are so arrangedthat their focal planes coincide with those of the 5 objectives, andwhen measuring marks -at difierent apparent distances are used, thedifferent distances which obtain between the eye-pieces and the marksand are due to the4 inclination of the planes containing the marksmake-it neces- 10 sary to vary the axial adjustmentsof the eyepieces assoon as the capacity of adaptationjof the observers eyes fails toneutralize these differences. Axial adjustments of the eye-pieces can,however, be dispensedwith yin the measure- 15 ment of objects atdiiie'rent, distances when the mark carriers are wedge-shaped plateseach of which consists of two glass Wedges traversed subsequently toeach other by the imaging rays and' whose cemented surfaces carry themarks, and 2o when the wedges traversed -last have .such refractingangles that the cemented surfaces appear to lle in planes parallel tothe focal planes of the objectives and the eye-pieces. In case the lastsaid condition is fulfilled only approximately, 25'

the adaptation of the. observers eyes will be suillcient, as a rule, andnot need the help of axial adjustments of the eye-pieces. Thewedgeshaped mark carriers, however, deviate the pencil of rays in such amanner that theimage plane does not appear to be at. right angles .tothe axes of the pencils of imaging rays. How these reciprocal positionsare reinstated has been treated repeatedly in the literature of the artand is therefore considered as known.

In lthe accompanying drawing, which lillustrates a constructionalexample of a stereo- 4scopic rangefinder according to the invention,Figure 1 shows the rangefinder in plan view section and Figures 2 and 3represent diiferent 40A forms of single optical line A-A in Figure l.

The rangeflnder has a housing a. Inthis housing are provided twowindowsb whose. distance apart corresponds to the base length and 45 behindwhich pentagonal prisms c are disposed whose reflecting surfaces ,are inthe shape ofroofs. These prisms c deiiect at right angles the pencils ofimaging rays entering the windows b and direct them to objectives dwhich 5 combine all incident pencils of parallel imaging rays in planese at a small distance behind the ray exit surfaces f of triangularprisms a. Rlano-parallel platesy are cemented to the ray exit surfaces fin the manner shown by Figure 2,- 55

parts in sections through each of these plates consisting of twowedgeshaped glass prisms hand i and having measuring marks 7c on theirinclined cemented surfaces. The measuring marks k are viewed by means(of adjustable eye-pieces l.

The known stereoscopic' combination `oi.the

marks 7c in pairs p rovides stereoscopic measuring marks at definiteapparent distances. The marks k are sodisposed on the inclined cementedsurfacesv of the plates that the planes of the marks, which are'parallel to the focal planes e of the objectives, correspond to theplanes in which the objectives d at corresponding distances. On accountof the refraction due to the wedges i, an observer looking into theeye-pieces l perceives the cemented surfaces'as lying in the surface mindicated in the drawing by dotted llines. Also this surface m isinclined to the focal tives d and the eye-pieces l. Accordingly; whenthe different marks k are looked at, the eye-pieces l require to beadjusted axially if these differences in the positions of the marks kcannot be neutralized by the capacity of adaptation of the observerseyes.

The said disadvantage can be ing plates according to Figure the form ofwedges, of two glass wedges having inclined cemented surfaces. The oneglass wedge of each plate corresponds to the wedges h of the exampleillustrated by Figure 2. The other glass wedge of each plate, which isdesignated n, has a refracting angle greater than that of the wedges iaccording to Figure 2 and is so constructed that the inclined cementedsurfaces appear to lie in planes avoided by us- 3, which are in imagethe objects lying planes of the objecand each of which consists oparallel to the focal planes of the objectives and the eye-pieces.

I claim:

1. A stereoscopic rangeflnder having a housing, this housing beingprovided with two stationary objectives and two eye-pieces displaceablein the directions reflecting systems for displacing the pencils ofimaging rays of the said objectives parallel to themselves, stationarymeasuring marks disposed in the said housing and ing those of the imagesproduced by the said objectives which correspond to objects whosedistances from the rangefinder correspond 'to -the apparent distances ofstereoscopic marks due to combination in pairs of the said measuringmarks, these measuring marks lying in two planes inclined to the focalplanes of the two objectives, respectively, and two mark carriersdisposed in the said housing, one of the surfaces of each mark' carriercoinciding respectively with these last said planes.

2. In a stereoscopic rangender according to claim 1, each of the saidcarriers consisting of plano-parallel plates fixed into the saidhousing, each of these plates consisting of two wedgeshaped partscemented together, and the said measuring marks being disposed on thecemented surfaces of the said parts. A I

3. In a stereoscopic rangender according to claim 1, each of the saidcarriers consisting of wedge-shaped plates xed'into the said housing,each of these plates consisting of two wedgeshaped parts cementedtogether, and the measuring marks being disposed on the cementedsurfaces of the said parts.

OTIO EPPENSTEIN.

of their optical axes, twol lying in planes contain-

